Thin magnetic films deposited (e.g., by physical-vapor deposition processes such as plasma sputtering and ion-beam deposition methods) onto substrates in low-pressure processing environments can be magnetically oriented to a single axis, a condition referred to as xe2x80x9cuniaxial anisotropyxe2x80x9d, by exposing the films to orienting magnetic fields with sufficient field strength that exhibit high magnetic flux uniformity and little angular skew on the substrate during the deposition or subsequent post-deposition processing of the films (such as magnetic annealing processes). Magnetic orientation of thin films can take place in conjunction with various applications including thin-film deposition and thermal anneal processes as well as thin-film magnetic metrology.
Thin-film magnetic recording heads are usually fabricated using a combination of material layers including one or more layers of thin soft and hard magnetic films, some of which may have magnetic domains oriented along one or multiple magnetic axes. Generally, the magnetic films are deposited onto substrates in low-pressure processing chambers by physical-vapor deposition (PVD) methods such as plasma sputtering or ion-beam deposition processes. The magnetic domains of these films are oriented by exposing the films to in-plane magnetic fields either during their deposition or during a subsequent processing step such as magnetic annealing. The magnetic fields have specific requirements specifying the upper limits for both xe2x80x9cskewxe2x80x9d (deviation in direction) and xe2x80x9cnon-uniformityxe2x80x9d (deviation in magnitude). Typical in-plane magnetic field strengths are in the range of 50 to 100 Oersted.
Either permanent magnets or electromagnets can be used for generating the substantially uniaxial magnetic fields. For example, Nakagawa et al. in U.S. Pat. No. 4,865,709 mount thin magnetic film substrates between pairs of permanent magnets on a substrate holder. Opposite poles of the magnets face each other for generating approximately uniaxial magnetic fields across the thin film surfaces of the substrates. However, the permanent magnets are difficult to position, have limited magnetic field strength and adjustability, and are exposed to processing that can affect their long-term performance (resulting, for instance, in long-term field drift). Permanent magnets may also have detrimental effects on the PVD plasma uniformity and repeatability. Moreover, permanent magnets provide no or limited capability for field magnitude or orientation adjustments.
Setoyama et al. in U.S. Pat. No. 4,673,482 position a pair of magnetic field-generating coils on opposite sides of a substrate outside a low-pressure processing chamber in which the substrate is mounted. The coils are located at a considerable distance from the substrate and only a small portion of the resulting magnetic field exhibits the required uniaxial characteristics. Magnetic field adjustability is also limited. Moreover, this type of magnetic field source can produce significant plasma non-uniformity and magnetic interference problems associated with magnetron PVD energy sources.
Co-assigned U.S. Pat. No. 5,630,916 to Gerrish et al., which names one of the inventors of this invention, overcomes many of these problems by positioning a plate-shaped electromagnet adjacent to the substrate positioned over a substrate support. The plate-shaped electromagnet is isolated from the processing environment by the substrate support (i.e., electromagnet located outside the vacuum processing chamber) but is still close to the substrate. The substantially planar plate-shape of the electromagnet, which parallels the substrate, produces a uniaxial field of high uniformity and relatively low skew in the immediate vicinity of the substrate surface. An angularly adjustable support provides for mechanically orienting the plate-shaped electromagnet with respect to the substrate support for fine tuning the magnetic orientation axis.
More recently, tolerances for magnetic field skew (angular deviation from the preferred orientation axis) and non-uniformity have become increasingly stringent and the size of the substrates has become increasingly large (up to 6xe2x80x3xc3x976xe2x80x3 square substrates).
Both trends pose similar problems for the available magnetic field orienting equipment. Larger electromagnets can be used to some extent. However, various practical considerations limit the size of the electromagnets. For example, Gerrish et al.""s electromagnet is required to fit within a substrate holder, which is itself limited in size by surrounding vacuum processing chamber dimensions. Unused portions of the magnetic fields produced by the larger magnets beyond the substrate surface area can interfere with substrate processing such as by altering the path of ions to the substrate (thus causing plasma process uniformity degradation) or imbalancing target erosion (e.g., via magnetic field interference with the PVD magnetron energy source).
The invention involves modifications to the core of plate-shaped electromagnets (i.e., core engineering) for enhancing the magnetic processing performance of thin films by reducing angular skew and non-uniformity of uniaxial magnetic fields produced by the orienting electromagnets. The modifications include redistributions of magnetic mass or magnetic qualities of the magnetic mass within the electromagnet core. Preferred redistributions take place in patterns that are centered within the core.
The invention can be practiced in various ways including in-situ magnetic orientation in low-pressure PVD (such as plasma sputtering and ion-beam deposition) and in magnetic thermal annealing processing systems. A thin-film processing electromagnet for practicing the invention has a plate-shaped core containing magnetically permeable material. Substantially parallel front and back surfaces of the plate-shaped core are joined by a generally polygonal periphery, and electrically conductive windings are wrapped around a region of the plate-shaped core forming at least one electromagnetic coil for producing a substantially uniaxial magnetic field adjacent to the front surface of the plate-shaped core.
The magnetically permeable material of the plate-shaped core has a mass with an effective magnetic mass density that can vary within the region wrapped by the electrically conductive windings from a center toward the periphery of the plate-shaped core for reducing a skew angle and improving uniformity of the substantially uniaxial magnetic field adjacent to the front surface of the plate-shaped core. The effective magnetic mass variation generally involves a reduction in the mass of the magnetically permeable material near the center of the core with respect to the mass of the magnetically permeable material near the periphery of the core. Also, the magnetic mass variation is preferably patterned with at least one axis of symmetry that extends through the center of the plate-shaped core.
The preferred way of achieving the desired effective magnetic mass variation is by forming a cavity in the plate-shaped core. The cavity can be formed through either the front surface or the back surface of the core, or it can be embedded as a through cavity within the core between the front and back surfaces of the core. Good results have been obtained by centering the cavity within the core and by conforming the peripheral shape of the cavity to the shape of the core periphery. For example, both the cavity and the core periphery can have matching polygonal (e.g., square) shapes.
The magnetically permeable material of the plate-shaped core has an effective magnetic permeability that can also vary within the region wrapped by the electrically conductive windings from a center toward the periphery of the plate-shaped core. The windings are wrapped between two winding planes of the plate-shaped core, and the effective magnetic permeability measured between the winding planes may be varied along the winding planes in a pattern that reduces angular skew and improves uniformity of the uniaxial magnetic field.
Both material composition and geometrical dimensions of the core can affect the effective magnetic permeability measured between or within the winding planes. For example, the core can include a variation in the concentration of a single magnetic material or in the distributions of more than one magnetic material. A cavity reduces the effective magnetic permeability between winding planes by creating a gap that can be left empty or filled by either a non-magnetic material or a lower magnetic permeability material.